Lenticular overlays are a known means to give images the appearance of depth. A lenticular image is created using a transparent upper layer having narrow, parallel lenticules (semi-cylindrical lenses) on an outer surface, and an image-containing substrate which projects images through the lenticules. The two layers form a lenticular system wherein different portions of an image are selectively visible as a function of the angle from which the system is viewed. If the image is a composite picture made by bringing together into a single composition a number of different parts of a scene photographed from different angles, and the lenticules are vertically oriented, each eye of a viewer will see different elements and the viewer will interpret the net result as depth of field. The viewer may also move his head with respect to the image thereby observing other views with each eye and enhancing the sense of depth.
Another method for showing images is the use of a blocking line screen positioned at a specific distance from the composite picture. This parallax process causes blocking of all images except one specific image. This allows the eyes to view different images as three-dimensional (3-D) images, or to achieve a simulation of motion, by the process of tipping the medium or movement of the head to a different angle with respect to the medium. Both of these processes, a lenticular image or a line blocking screen, can be used to generate a 3-D effect at a proper viewing distance, or simulated motion multiple images, by viewing the composite image from different angles.
When the lenticules or blocking line screen is oriented horizontally, each eye receives the same image. In this case, the multiple images give illusion of motion when the composite image is rotated about a line parallel to a line formed by the viewers eyes.
Whether the lenticules or the line blocking screen is oriented vertical or parallel, each of the viewed images are generated by lines of images which have been interlaced at the frequency of the lenticular or line blocking screen. Interlacing lines of each image is referred to as interdigitation. Interdigitation can be better understood by using an example four images used to form a composite with a material having three lenticules. In this example, line 1 from each of the four images is in registration with the first lenticule; line 2 from each of the four images is in registration with the second lenticule; etc. Each lenticule is associated with a plurality of image lines or an image line set, and the viewer sees only one image line of each set with each eye for each lenticule. It is imperative that the line image sets be registered accurately with respect to the lenticules, so that the proper picture is formed when the assembly is viewed.
Conventional recording of linear images on a lenticular recording material has been accomplished with a stereoscopic image recording apparatus that uses optical exposure. A light source, such as a halogen lamp, is projected through an original image, through a projection lens, and focused on lenticular material. The images are exposed on a receiver attached to the lenticular material as linear images. Japanese (Kokoku) Patent Applications Nos. 5473/1967, 6488/1973, 607/1974, and 33847/1978 disclose recording apparatus in which two original images are projected for printing on a lenticular recording material. Recording composite images in this fashion requires complex lens structures, which are expensive.
In contrast, image recording by scanning exposure requires comparatively simple optics, has great flexibility in adapting to various image processing operations, and to alterations in the dimension of the lenticules. To take advantage of these features, various apparatus and methods have been proposed for recording image by scanning exposure. For example, Japanese (Kokoku) Patent Application No. 3781/1984 teaches a stereoscopic image recording system in which a plurality of original images is taken with a TV camera, processed and stored in frame memories from which the stored image signals are retrieved sequentially as linear images in accordance with the pitch of lenticular lenses used. After the linear images are recorded on a recording material by scanning exposure, the lenticular sheet is bonded to the recording material. Another scanning method uses polygon scanners, described in U.S. Pat. No. 5,349,419, for exposure of photosensitive stereoscopic images directly on lenticular materials.
One of the problems associated with using polygon scanners for printing interdigitized images is the introduction of banding in the image. One cause of banding is due to differences in the reflectance for each facet of the polygon. One method to alleviate this problem is detailed in U.S. Pat. No. 5,248,997 which relates to using a lookup table to make the necessary corrections. This method, although effective, requires calibration and extra time to make the appropriate lookups of data from a table. Other causes of banding are slight differences in the polygon center-to-facet distance, and the lack of parallelism of each facet of the polygon to the spin axis.